Optical splicer, optical module, and method of producing optical splicer

ABSTRACT

An optical splicer  2  according to an embodiment of the present invention has a plurality of optical fibers  6 , and an optical splice member  8  having a plurality of fiber holes  14  in each of which a portion including one end  6   a  of each fiber  6  is inserted, and a mode field diameter W 1  in one end  6   a  of optical fiber  6  is enlarged relative to a mode field diameter W 2  in the other portion of optical fiber  6.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical splicer for splicing opticalfibers, an optical module, and a method of producing the opticalsplicer.

2. Related Background of the Invention

There are optical splicers for splicing optical fibers by inserting theoptical fibers in glass capillaries face to face.

For example, Japanese Patent No. 3154230 describes the optical splicerfor splicing a plurality of optical fibers, which comprises a pluralityof glass capillaries. In this optical splicer, the central region ofeach glass capillary is preliminarily filled with an index matchingagent.

Japanese Patent Publication No. 7-50219 describes the optical splicer inwhich a predetermined space is provided between end faces offace-to-face optical fibers and in which the space is filled with anelastic adhesive to effect a splice of the optical fibers.

SUMMARY OF THE INVENTION

In the aforementioned optical splicer described in Japanese Patent No.3154230, where the end face of each fiber is not in a good state (i.e.,where each optical fiber is not accurately cut at the end face), therewill arise axial misalignment or a clearance between end faces ofoptical fibers. In consequence, a splice loss will be large in theoptical splice with partner fibers.

In the aforementioned optical splicer described in Japanese PatentPublication No. 7-50219, the space is provided between end faces ofoptical fibers. Since an optical signal emerging from an optical fiberdivergently propagates in this space, the splice loss must also belarge.

An object of the present invention is therefore to provide an opticalsplicer capable of reducing the splice loss in collective splicing ofmultiple optical fibers, an optical module, and a method of producingthe optical splicer.

An optical splicer according to the present invention is an opticalsplicer comprising: a plurality of optical fibers; and an optical splicemember having a plurality of fiber holes in each of which a portionincluding one end of each optical fiber is inserted; wherein a modefield diameter in the one ends of the optical fibers is enlargedrelative to a mode field diameter in the other portions of the opticalfibers.

When the optical splicer of this configuration is used to implementcollective splicing of multiple fibers, the optical fibers are insertedfrom both sides of the fiber holes of the optical splice member so as toface each other. Since the mode field diameter in the one ends of theoptical fibers (the ends to be spliced with partner optical fibers) isenlarged relative to the mode field diameter in the other portions ofthe optical fibers, the numerical aperture (NA) of the optical fibers issmall, so as to suppress the spread of light propagating between theoptical fibers facing each other in the fiber holes. For this reason,even if there is a clearance or axial misalignment due to variations inangles of end faces and in positions of end faces between two opticalfibers facing each other, the fibers can be spliced with each other witha low loss. Therefore, the splice loss can be reduced in collectivesplicing of multiple fibers even if the end faces of the optical fibersare not cut with high accuracy.

Preferably, the portions including the one ends of two optical fibersare inserted in each of the fiber holes so as to face each other fromboth sides of the optical splice member and a space between end faces ofthe two optical fibers facing each other in the fiber holes is filledwith an adhesive having a refractive index matched with a refractiveindex of cores of the optical fibers. Since in this case the spacebetween the end faces of two facing fibers is filled with the adhesivehaving the refractive index matched with that of the cores of theoptical fibers, reflection of light can be suppressed in the spacebetween two facing fibers. This can reduce the splice loss more incollective splicing of multiple fibers.

Preferably, the portions including the one ends of the optical fibersare inserted in the fiber holes from only one side of the optical splicemember and end faces of the optical fibers are covered by an adhesive inthe fiber holes. When the end faces of the optical fibers are covered bythe aforementioned adhesive in the fiber holes as in this configuration,the end faces are coated with an antireflection coating. Namely, lightemerging from the end faces of optical fibers is scattered by theadhesive layer, which can prevent the light from returning as reflectedlight to the optical fibers.

Preferably, the adhesive is an ultraviolet-curable adhesive and theoptical splice member is made of a material that transmits ultravioletlight. In this configuration, the adhesive can be cured, for example,under irradiation with ultraviolet light supplied from the outside ofthe optical splice member, so that the end faces of the optical fibersfacing each other in the fiber holes can be bonded to each other withoutdifficulties and in a short time.

Preferably, the optical splice member comprises a substrate having guidegrooves for guiding the one ends of the optical fibers, and a retainermounted on the substrate, for retaining the portions including the oneends of the optical fibers, against the substrate, and the fiber holesare formed by the guide grooves and the retainer. In this case, forexample, if the retainer is constructed so as to cover the region exceptfor the both ends of the guide grooves in the upper surface of thesubstrate, the one ends of the optical fibers can be inserted along theguide grooves into the fiber holes. Therefore, the optical fibers can bereadily inserted into the fiber holes.

Preferably, the plurality of optical fibers is comprised of an opticalfiber ribbon of multiple fibers, and the portions including the one endsof the optical fibers are a part exposed by removing a coating of theoptical fiber ribbon. The use of the optical fiber ribbon facilitatesconstruction of an optical module incorporating multiple optical fibers.

An optical module according to the present invention is an opticalmodule comprising: the optical splicer as set forth; and at least oneoptical device having an optical waveguide optically connected to theother end of each optical fiber. When the optical splicer is provided inthis manner, the optical fibers can be spliced with each other with alow loss even if there is a clearance or axial misalignment due tovariations in angles of end faces and in positions of end faces betweentwo facing optical fibers, as described above.

A production method of an optical splicer according to the presentinvention is a method of producing an optical splicer, the methodcomprising: a step of removing a part of a coating of an optical fiberribbon of multiple fibers to expose a plurality of optical fibers; astep of enlarging a mode field diameter of the optical fibers; a step ofcutting portions with the enlarged mode field diameter in the opticalfibers; and a step of inserting the optical fibers into fiber holes ofan optical splice member, after the step of cutting the optical fibers.

By this production method, the portions where the mode field diameter isenlarged in the optical fibers are inserted into the fiber holes of theoptical splice member. For this reason, where two optical fibers arebrought into a face-to-face state in each fiber hole, the optical fiberscan be spliced with each other with a low loss even if there is aclearance or axial misalignment due to variations in angles of end facesand in positions of end faces between two facing fibers, as describedabove. Therefore, the splice loss can be reduced in collective splicingof multiple fibers even if the end faces of the fibers are not cut withhigh accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view including a sectional view in part, which shows anoptical module incorporating an embodiment of the optical spliceraccording to the present invention.

FIG. 2 is a vertical sectional view of the optical module shown in FIG.1.

FIG. 3 is a sectional view along line III-III in FIG. 1.

FIG. 4 is a vertical, enlarged, sectional view of the optical splicer.

FIG. 5 is an illustration showing production steps of optical splicer 2.

FIG. 6 is a graph showing the relationship among the mode field diameterin one ends of two facing fibers, the distance between end faces in theone ends of the two optical fibers, and the splice loss.

FIG. 7 is a plan view showing an optical module incorporating anotherembodiment of the optical splicer according to the present invention.

FIG. 8 is a vertical, enlarged, sectional view showing the major part ofthe optical splicer shown in FIG. 7.

FIG. 9 is a plan view showing an optical module incorporating stillanother embodiment of the optical splicer according to the presentinvention.

FIG. 10 is a plan view showing an optical module incorporating stillanother embodiment of the optical splicer according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the optical splicer, the optical module,and the production method of the optical splicer according to thepresent invention will be described below with reference to thedrawings.

FIG. 1 is a plan view including a cross section in part, which shows anoptical module incorporating an embodiment of the optical spliceraccording to the present invention, FIG. 2 a vertical sectional view ofthe optical module shown in FIG. 1, and FIG. 3 a sectional view alongline III-III in FIG. 1. FIG. 4 is a vertical, enlarged, sectional viewof optical splicer 2.

As shown in each figure, the optical module 1 of the present embodimenthas an optical splicer 2 and two optical devices 4. The optical splicer2 is a device for splicing two optical devices 4 with each other.

The optical splicer 2 has an optical splice member 8 for collectivelysplicing a plurality of optical fibers 6 with a plurality of partnerfibers 6. The plurality of optical fibers 6 are, for example,single-mode optical fibers. The plurality of optical fibers 6 areconstructed in the form of optical fiber ribbon 6 x of multiple fibers.The coating is removed from the both ends of the optical fiber ribbon 6x, to expose each optical fiber 6. As shown in FIG. 4, the mode fielddiameter (core diameter) W1 in one ends 6 a of optical fibers 6 isenlarged relative to the mode field diameter W2 in the other portions ofoptical fibers 6. More specifically, the mode field diameter W2 isapproximately 10 μm, whereas the mode field diameter W1 is at mostapproximately 20-40 μm. This enlargement of the mode field diameter isimplemented by heating the optical fibers 6 (as will be describedlater).

The optical splice member 8 is composed of a fiber array substrate 8 aand a retainer 8 b. The fiber array substrate 8 a and the retainer 8 bare made, for example, of a material such as glass which readilytransmits ultraviolet light.

As shown in FIG. 3, a plurality of V-shaped guide grooves 10 forretaining and positioning optical fibers 6 are provided in the uppersurface of the fiber array substrate 8 a. In addition, positioninggrooves 11 for accommodating positioning pins 9 are provided on bothsides of the guide grooves 10 in the upper surface of the fiber arraysubstrate 8 a. The positioning pins 9 are pins for positioning theretainer 8 b relative to the fiber array substrate 8 a, and have theouter diameter equal to or slightly larger than the outer diameter ofthe optical fibers 6. The positioning grooves 11 are also formed inV-shape as the guide grooves 10 are. This facilitates the fabrication ofthe fiber array substrate 8 a including the guide grooves 10 andpositioning grooves 11.

The retainer 8 b is located so as to cover part of the optical fibers 6placed on the fiber array substrate 8 a, and is provided with aplurality of V-shaped retaining grooves 12 corresponding to the guidegrooves 10 and positioning grooves 11. The retainer 8 b is fixed to thefiber array substrate 8 a, for example, with an adhesive. The guidegrooves 10 of the fiber array substrate 8 a and the retaining grooves 12of the retainer 8 b form fiber holes 14 in which respective fibers 6 areinserted.

As shown in FIG. 4, one ends 6 a of two optical fibers 6 are inserted ineach fiber hole 14 so as to face each other from both sides of opticalsplice member 8. The space between the end faces of one ends 6 a of twooptical fibers 6 is filled with a UV-Curable adhesive 13 having therefractive index matched with that of the cores of the optical fibers 6.The UV-curable adhesive 13 is comprised of a material such as epoxyresin or acrylic resin, for example. This UV-curable adhesive 13 alsofills the space between the optical splice member 8 and the opticalfibers 6. The UV-curable adhesive 13 is cured with ultraviolet lightsupplied from the outside of the optical splice member 8, so that theend faces in one ends 6 a of two optical fibers 6 and, the opticalsplice member 8 and optical fibers 6 are bonded to be fixed to eachother. By using the UV-curable adhesive 13 in this manner, the end facesin one ends 6 a of optical fibers 6 can be bonded to each other withoutdifficulties and in a short time.

As shown in FIG. 1, each optical device 4 comprises an optical fiberarray 15, a planar optical waveguide 16, and a housing 18. The opticalfiber array 15 and planar optical waveguide 16 are placed in the housing18. An optical fiber ribbon 6 x is introduced into the housing 18. Theoptical fiber array 15 holds the other ends 6 b of respective opticalfibers 6 exposed from the optical fiber ribbon 6 x. The planar opticalwaveguide 16 has a plurality of lightguide cores (not shown), theoptical fiber array 15 is fixed to the end face 16 a of the planaroptical waveguide 16, and the optical fibers 6 held by the optical fiberarray 15 are positioned relative to the lightguide cores.

FIG. 5 is an illustration showing production steps of optical splicer 2.It is assumed herein that an optical fiber ribbon 6 x is preliminarilyconnected to each optical device 4. The optical splicer 2 is producedaccording to the following procedure.

An ozone beam L1 is applied from above the optical fiber ribbon 6 x toetch the intermediate part of the optical fiber ribbon 6 x (FIG. 5(a)).This results in removing the coating from the intermediate part of theoptical fiber ribbon 6 x to expose the bare bodies (glass parts) ofmultiple optical fibers 6. Here the length of the exposed parts ofoptical fibers 6 (the length of the removed coating of the optical fiberribbon 6 x) is preferably 3-10 mm and more preferably 5-7 mm. By keepingthe bare bodies of optical fibers 6 short in this manner, it is feasibleto prevent the optical fibers 6 from being readily broken during theproduction process.

Subsequently, in order to enlarge the mode field diameter of exposedoptical fibers 6, the surfaces of the bare bodies of exposed opticalfibers 6 are heated by CO₂ laser L2 (FIG. 5(b)). Then the dopantcomponent in the cores of the exposed optical fibers 6 thermallydiffuses toward the cladding to change the index profile of the glassparts. This results in enlarging the mode field diameter of the exposedoptical fibers 6. In the case of the ordinary single-mode opticalfibers, it is possible to enlarge the mode field diameter up to 40 μm.The heating of the optical fibers 6 may be implemented by use of aburner or a heater, instead of the CO₂ laser L2.

Subsequently, the optical fibers 6 with the mode field diameter thusenlarged are cut at the position where the mode field diameter enlargedis maximum, by a cutter or the like (FIG. 5(c)). After the cutting,portions including one ends 6 a of optical fibers 6 are inserted intofiber holes 14 of optical splice member 8 so as to face partner opticalfibers 6 (FIG. 5(d)). Then the UV-curable adhesive 13 is poured into thefiber holes 14 from the both ends of the retainer 8 b, and the opticalfibers 6 are bonded to the partner optical fibers 6 and to the opticalsplice member 8 with this UV-curable adhesive 13.

Incidentally, the most common fiber splicing technology is the fusionsplice technology. The fusion splice technology requires the end facesof the optical fibers to be cut with high accuracy, in order toimplement low-loss splicing of optical fibers, and the fibers needs tobe spliced with failure in cutting of end faces (retrial) always inmind. Specifically, an extra length is always left in the optical fiberson the occasion of splicing the optical fibers with each other, so as toallow a splice work to be again performed using the extra length part ofthe optical fibers even if there occurs a failure in cutting the endfaces of optical fibers to cause a failure in fusion splicing. However,an extra storage space is necessary for securing the extra length ofoptical fibers, and thus, in the case of an optical module having aplurality of optical devices, a sufficient extra storage space has to beprovided, which will be great hindrance against miniaturization of theoptical module. Furthermore, there are restrictions on the bendingradius of the optical fibers (30 mm or less), and circumstances do notallow reduction of the extra storage space.

In contrast to it, since the present embodiment adopts the configurationwherein the mode field diameter in one ends 6 a of optical fibers 6 isenlarged, the numerical aperture of optical fibers 6 becomes smaller bythat degree, and light propagating between two optical fibers 6 is closeto parallel light. Since this suppresses dispersion of power density oflight, optical fibers 6 can be spliced with each other with a low losseven if there is a clearance or axial misalignment due to variations inangles of end faces and in positions of end faces between two facingfibers 6.

Since the space between two facing fibers 6 is filled with theUV-curable adhesive 13 having the refractive index matched with that ofthe cores of the optical fibers 6, the splice loss can be reduced moreand reflection of light can be reduced in the clearance between twooptical fibers. Therefore, good splice characteristics can be achievedeven with irregularities in the end faces of multiple fibers 6.Therefore, the present embodiment obviates the need for accuratelycutting the end faces of optical fibers 6 and the need for securing theextra length of the optical fibers 6 as in the fusion splice.

In addition, the length of the bare bodies of optical fibers 6 can beshorter in the process of enlarging the mode field diameter of opticalfibers 6 than in the case of discharge heating during the fusion splice,and thus the length of optical splice member 8 can be short. This canreduce the splice spacing between two optical devices 4, so that thesize of optical module 1 can be dramatically reduced.

FIG. 6 is a graph showing the relationship among the maximum of the modefield diameter (MFD) in one ends 6 a of two facing fibers 6, thedistance between end faces of one ends 6 a of the two fibers 6, and thesplice loss, in the aforementioned optical splicer 2. The graph of FIG.6 shows the case where the wavelength of the optical signal transmittedon the optical fibers 6 is 1.55 μm and where the refractive index ofoptical fibers 6 is 1.444. As shown in FIG. 6, the splice loss increaseswith increase in the distance between end faces of one ends 6 a of twooptical fibers 6. On the other hand, the rate of the increase of spliceloss decreases with increase in the maximum of the mode field diameter.For this reason, the mode field diameter is particularly preferablyenlarged so that the maximum thereof becomes not less than 30 μm. Inthis case, the splice loss is not more than 0.2 dB even if the distanceis 200 μm between end faces of one ends 6 a of two optical fibers 6.

FIG. 7 is a plan view showing an optical module incorporating anotherembodiment of the optical splicer according to the present invention,and FIG. 8 a vertical, enlarged, sectional view showing the major partof the optical splicer shown in FIG. 7. In the drawings, identical orequivalent members to those in the above-described embodiment aredenoted by the same reference symbols, without redundant descriptionthereof.

As shown in each figure, the optical module 100 of the presentembodiment has an optical splicer 200, and this optical splicer 200 hasan optical splice member 8 similar to that in the aforementionedembodiment. The optical splice member 8 collectively splices some ofmultiple fibers 6 with partner fibers 60 led out of optical device 62.Namely, the partner fibers 60 are constructed in the form of an opticalfiber ribbon 60 x including less optical fibers than those of theoptical fiber ribbon 6 x. The optical fibers 60 are inserted in some offiber holes 14 in the optical splice member 8. Namely, the opticalfibers 6 and optical fibers 60 are inserted in some of fiber holes 14 soas to face each other from both sides of the optical splice member 8,and only optical fibers 6 are inserted in the remaining fiber holes 14.In the fiber holes 14, the space between end faces of optical fibers 6and optical fibers 60 is filled with the UV-curable adhesive 13 asdescribed above.

In addition, the end faces of optical fibers 6 without connectionpartners in the fiber holes 14 are covered by the UV-curable adhesive13. As the end faces are covered by the UV-curable adhesive 13 in thismanner, the end faces of optical fibers 6 are coated with anantireflection coating. Therefore, light emerging from the end faces ofoptical fibers 6 is scattered by the layer of UV-curable adhesive 13,whereby the light is prevented from undergoing unwanted reflection onthe end faces of the optical fibers 6 and from returning to the opticalfibers 6.

The present invention can be modified in various ways, without having tobe limited to the above-described embodiments.

FIG. 9 is a plan view showing an optical module incorporating stillanother embodiment of the optical splicer according to the presentinvention. In FIG. 9, an optical splice member 8 of optical splicer 300collectively splices optical fibers 6 of an optical fiber ribbon 6 xwith optical fibers 70, 71 of optical fiber ribbons 70 x, 71 x. Theoptical fiber ribbons 70 x, 71 x are spliced with their respectiveoptical devices 72, 74.

FIG. 10 is a plan view showing an optical module incorporating stillanother embodiment of the optical splicer according to the presentinvention. In FIG. 10, an optical splice member 8 of optical splicer 400collectively splices optical fibers 80, 81 of optical fiber ribbons 80x, 81 x with optical fibers 70, 71 of optical fiber ribbons 70 x, 71 x.The optical fiber ribbons 80 x, 81 x are spliced with their respectiveoptical devices 82, 84, and the optical fiber ribbons 70 x, 71 x withtheir respective optical devices 72, 74.

In the above embodiments the optical splice member 8 was comprised ofthe fiber array substrate 8 a and the retainer 8 b, but the opticalsplice member may be comprised of an integrated combination of the fiberarray substrate and the retainer.

As the preferred embodiments of the present invention were describedabove, the present invention successfully achieves the reduction of thesplice loss in collective splicing of multiple fibers.

1. An optical splicer comprising: a plurality of optical fibers; and anoptical splice member having a plurality of fiber holes in each of whicha portion including one end of each optical fiber is inserted; wherein amode field diameter in the one ends of the optical fibers is enlargedrelative to a mode field diameter in the other portions of the opticalfibers.
 2. The optical splicer according to claim 1, wherein theportions including the one ends of two optical fibers are inserted ineach of the fiber holes so as to face each other from both sides of theoptical splice member and wherein a space between end faces of the twooptical fibers facing each other in the fiber holes is filled with anadhesive having a refractive index matched with a refractive index ofcores of the optical fibers.
 3. The optical splicer according to claim2, wherein the adhesive is an ultraviolet-curable adhesive and whereinthe optical splice member is made of a material that transmitsultraviolet light.
 4. The optical splicer according to claim 1, whereinthe portions including the one ends of the optical fibers are insertedin the fiber holes from only one side of the optical splice member andwherein end faces of the optical fibers are covered by an adhesive inthe fiber holes.
 5. The optical splicer according to claim 4, whereinthe adhesive is an ultraviolet-curable adhesive and wherein the opticalsplice member is made of a material that transmits ultraviolet light. 6.The optical splicer according to claim 1, wherein the optical splicemember comprises a substrate having guide grooves for guiding the oneends of the optical fibers, and a retainer mounted on the substrate, forretaining the portions including the one ends of the optical fibers,against the substrate, and wherein the fiber holes are formed by theguide grooves and the retainer.
 7. The optical splicer according toclaim 1, wherein the plurality of optical fibers is comprised of anoptical fiber ribbon of multiple fibers, and wherein the portionsincluding the one ends of the optical fibers are a part exposed byremoving a coating of the optical fiber ribbon.
 8. An optical modulecomprising: the optical splicer as set forth in claim 1; and at leastone optical device having an optical waveguide optically connected tothe other end of each optical fiber.
 9. A method of producing an opticalsplicer, the method comprising: a step of removing a part of a coatingof an optical fiber ribbon of multiple fibers to expose a plurality ofoptical fibers; a step of enlarging a mode field diameter of the opticalfibers; a step of cutting portions with the enlarged mode field diameterin the optical fibers; and a step of inserting the optical fibers intofiber holes of an optical splice member, after the step of cutting theoptical fibers.